Computer object code obfuscation using boot installation

• US 8,176,337 B2
• Filed: 03/12/2008
• Issued: 05/08/2012
• Est. Priority Date: 03/12/2008
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Ciet, Mathieu, Lerouge, Julien, Farrugia, Augustin J.
• Primary Examiner(s): Moorthy, Aravind
• Assistant Examiner(s): MEJIA, FELICIANO S
• Application Number:
  US12/047,207
• Publication Number:
  US 20090235089A1
• Time in Patent Office: 1,518 Days
• Field of Search: 713/190, 717/140
• US Class Current: 713/190
• CPC Class Codes: G06F 21/14 against software analysis or reverse engineering, e.g. by obfuscation
• CPC Class Codes: G06F 21/577 Assessing vulnerabilities and evaluating computer system security

Abstract

In the field of computer software, obfuscation techniques for enhancing software security are applied to compiled (object) software code. The obfuscation results here in different versions (instances) of the obfuscated code being provided to different installations (recipient computing devices). The complementary code execution uses a boot loader or boot installer-type program at each installation which contains the requisite logic. Typically, the obfuscation results in a different instance of the obfuscated code for each intended installation (recipient) but each instance being semantically equivalent to the others. This is accomplished in one version by generating a random value or other parameter during the obfuscation process, and using the value to select a particular version of the obfuscating process, and then communicating the value along with boot loader or installer program software. This boot loader then selects which particular process to use for the code execution at the time of installation in accordance with the value. This results in different versions of the obfuscated code being provided to each recipient installation, which further enhances security of the code against reverse engineering by hackers.

Claims

1. A method of protecting computer program code, comprising the acts of:

providing a file of computer program source code;

storing the file in a first computer readable memory;

compiling the stored file of source code into compiled code at a compiler;

obfuscating the compiled code, using one of a plurality of obfuscation processes wherein the obfuscation processes are each one of a Montgomery multiplication, a Quisquater multiplication, and a Barrett multiplication;

providing a boot installer program including a plurality of deobfuscation processes, one of which is complementary to the one obfuscation process;

storing the boot installer program in a second computer readable memory;

combining the obfuscated code and the boot installer program into one file; and

storing the one file in a third computer readable memory.

2. The method of claim 1, further comprising the act of masking the obfuscated code.

3. The method of claim 1, wherein the obfuscated code when executed is equivalent but not identical to the compiled code.

4. The method of claim 1, further comprising the acts of:

generating a random number;

selecting the one obfuscation process for the act of obfuscating based on the random number; and

associating the random number with the obfuscated code.

5. The method of claim 4, wherein the obfuscation processes are each a different order for performing a plurality of functions in the compiled code, and wherein the random number determines the particular order.

6. The method of claim 4, where in the obfuscation processes are each equivalent to one another;

and

further comprising selecting one of the obfuscation processes for each instance of the obfuscated code using the value of the random number, wherein each such instance uses a different one of the obfuscation processes.

7. The method of claim 1, further comprising the act of:

selecting the one obfuscation process based on a characteristic of a target device.

8. The method of claim 1, wherein a plurality of Montgomery multiplication processes are provided, using coarsely integrated operand scanning and one using finely integrated operand scanning.

9. The method of claim 8, wherein a plurality of coarsely integrated operand scanning processes are provided, each having a base value of a different length.

10. Apparatus for protecting computer code, comprising:

a memory for storing a file of computer program source code;

a compiler coupled to the memory for compiling the source code into compiled code;

an obfuscator coupled to the compiler to output obfuscated code, using one of a plurality of obfuscation processes wherein the obfuscation processes are each one of a Montgomery multiplication, a Quisquater multiplication, and a Barrett multiplication;

a memory storing a boot installer program including a plurality of deobfuscation processes, one of which is complementary to the one obfuscation process;

an assembler which combines the obfuscated code and the boot installer program into one file; and

a third computer readable memory for storing the one file.